detect-newline 3.1.0: detect dominant newline character in string

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: detect dominant newline character in string
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/detect-newline@3.1.0
Demonstrate these symbols/APIs:
  - detectNewline
  - detectNewlineGraceful

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:1164809ff0597a2a7f5f8d7e8f1f92911a83ec8912ed7ae97851bd25752239b8","contract":["detectNewline returns \\r\\n when CRLF is the dominant newline character","detectNewline returns \\n when LF is dominant or when LF and CRLF counts are equal","detectNewline returns undefined when the string contains no newlines","detectNewline throws TypeError when called with a non-string argument","detectNewlineGraceful returns dominant newline character or defaults to \\n when no newline is present","detectNewlineGraceful returns \\n gracefully for non-string inputs without throwing"],"goal":"detect dominant newline character in string","kind":"HOW","packages":["pkg:npm/detect-newline@3.1.0"],"schemaVersion":1,"symbols":["detectNewline","detectNewlineGraceful"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/detect-newline@3.1.0"],"schemaVersion":1,"subject":"pkg:npm/detect-newline@3.1.0","symbols":["detectNewline","detectNewlineGraceful"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-detect-newline",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-detect-newline",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "detect-newline": "3.1.0"
      }
    },
    "node_modules/detect-newline": {
      "version": "3.1.0",
      "resolved": "https://registry.npmjs.org/detect-newline/-/detect-newline-3.1.0.tgz",
      "integrity": "sha512-TLz+x/vEXm/Y7P7wn1EJFNLxYpUD4TgMosxY6fAVJUnJMbupHBOncxyWUG9OpTaH9EBD7uFI5LfEgmMOc54DsA==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-detect-newline",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "detect-newline": "3.1.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "detect dominant newline character in string",
  "kind": "HOW",
  "packages": [
    "pkg:npm/detect-newline@3.1.0"
  ],
  "symbols": [
    "detectNewline",
    "detectNewlineGraceful"
  ]
}

import detectNewline from 'detect-newline';

const detectNewlineGraceful = detectNewline.graceful;

/**
 * Detect the dominant newline character of a string.
 * @param {string} string - The input string to inspect.
 * @returns {'\r\n' | '\n' | undefined} The dominant newline character or undefined.
 */
export function detect(string) {
  return detectNewline(string);
}

/**
 * Detect the dominant newline character of a string, defaulting to '\n' on missing or invalid input.
 * @param {unknown} [string] - The input to inspect.
 * @returns {'\r\n' | '\n'} The dominant newline character or '\n'.
 */
export function detectGraceful(string) {
  return detectNewlineGraceful(string);
}

export { detectNewline, detectNewlineGraceful };
export default detectNewline;

import assert from 'node:assert/strict';
import { detectNewline, detectNewlineGraceful, detect, detectGraceful } from '../src/index.mjs';

// 1. detectNewline returns \r\n when CRLF is the dominant newline character
{
  assert.equal(detectNewline('foo\r\nbar\r\nbaz\n'), '\r\n');
  assert.equal(detectNewline('\r\n\r\n'), '\r\n');
  assert.equal(detectNewline('line1\r\nline2\r\nline3\nline4\r\n'), '\r\n');
  assert.equal(detect('header\r\nbody\r\nfooter\n'), '\r\n');
}

// 2. detectNewline returns \n when LF is dominant or when LF and CRLF counts are equal
{
  assert.equal(detectNewline('foo\nbar\nbaz\r\n'), '\n');
  assert.equal(detectNewline('foo\nbar\n'), '\n');
  assert.equal(detectNewline('foo\r\nbar\n'), '\n');
  assert.equal(detectNewline('a\r\nb\nc\r\nd\n'), '\n');
  assert.equal(detect('first\nsecond\r\nthird\n'), '\n');
}

// 3. detectNewline returns undefined when the string contains no newlines
{
  assert.equal(detectNewline('foo bar baz'), undefined);
  assert.equal(detectNewline(''), undefined);
  assert.equal(detectNewline('   '), undefined);
  assert.equal(detect('single-line text without breaks'), undefined);
}

// 4. detectNewline throws TypeError when called with a non-string argument
{
  assert.throws(() => detectNewline(null), {
    name: 'TypeError',
    message: 'Expected a string'
  });
  assert.throws(() => detectNewline(undefined), {
    name: 'TypeError',
    message: 'Expected a string'
  });
  assert.throws(() => detectNewline(123), {
    name: 'TypeError',
    message: 'Expected a string'
  });
  assert.throws(() => detectNewline({}), {
    name: 'TypeError',
    message: 'Expected a string'
  });
  assert.throws(() => detectNewline(['\n']), {
    name: 'TypeError',
    message: 'Expected a string'
  });
  assert.throws(() => detect(true), {
    name: 'TypeError',
    message: 'Expected a string'
  });
}

// 5. detectNewlineGraceful returns dominant newline character or defaults to \n when no newline is present
{
  assert.equal(detectNewlineGraceful('foo\r\nbar\r\nbaz\n'), '\r\n');
  assert.equal(detectNewlineGraceful('foo\nbar\nbaz\r\n'), '\n');
  assert.equal(detectNewlineGraceful('foo bar baz'), '\n');
  assert.equal(detectNewlineGraceful(''), '\n');
  assert.equal(detectGraceful('single line text'), '\n');
  assert.equal(detectGraceful('multi\r\nline\r\ntext'), '\r\n');
}

// 6. detectNewlineGraceful returns \n gracefully for non-string inputs without throwing
{
  assert.equal(detectNewlineGraceful(null), '\n');
  assert.equal(detectNewlineGraceful(undefined), '\n');
  assert.equal(detectNewlineGraceful(), '\n');
  assert.equal(detectNewlineGraceful(123), '\n');
  assert.equal(detectNewlineGraceful({}), '\n');
  assert.equal(detectNewlineGraceful(['\r\n']), '\n');
  assert.equal(detectNewlineGraceful(false), '\n');
  assert.equal(detectGraceful(null), '\n');
}

console.log('All contract tests passed.');